Field of the Invention and Related Application
This invention relates to the treatment of exhaust gases and more particularly, to a filter medium for effectively treating gases which are discharged in large amounts for municipal refuse incineration plants and which contain fly ashes from incinerators, hydrogen chloride, nitrogen oxides, sulfur oxides and the like.
The present inventors have already developed and proposed a technique for forming a solid layer of slaked lime and clacium chloride on a woven filter fabric in order to efficiently eliminate hydrogen chloride from exhaust gases. The filter fabric used in this technique is made of a glass wool material which has a relatively poor heat resistance. Accordingly, it is necessary that a gas passed through the fabric be kept at a temperature lower than 250.degree. C.
Known heat-resistant filter materials include woven filter fabrics of carbon fibers and stainless steel wires. However, these fabrics have the disadvantage in that the carbon fiber-woven filter fabric is not resistant to abrasion and the stainless steel woven filter fabric is very expensive.
Although the present invention contemplates to eliminate not only hydrogen chloride, but also nitrogen oxides (i.e. denitration), it is difficult to deposit a catalyst for denitration on the stainless steel woven filter fabric in order to impart the denitration function. More particularly, for the coating of the denitration catalyst on the fabric surface, it is necesasry that the coating material (denitration catalyst) and the fabric surface be wetted sufficiently, but the stainless steel filter fabric has poor wettability, so that it is difficult to form a uniform coating layer on the fabric.